The present invention concerns a magnetic body device and a manufacturing method thereof.
A magnetic memory, particularly, a magnetic random access memory (MRAM) is prospective as a non-volatile memory capable of high speed operation and infinite times of rewriting and has been developed vigorously in recent years. MRAM uses a magnetic body as a memory device and stores data corresponding to the direction of magnetization of the magnetic body. For writing data into the magnetic memory, it is necessary to change the direction of magnetization in the magnetic body.
While various methods have been known as a switching method of magnetization direction of the magnetic body, a method of utilizing spin-orbit coupling has been proposed in recent years (for example, refer to Japanese Unexamined Patent Publication No. 2009-239135 (Patent document 1), Miron et al., “Current-driven spin torque induced by the Rashba effect in a ferromagnetic metal layer”, Nature Materials, Vol. 9, p230, 2010, (hereinafter referred to as Non-patent document 1), and Miron et al., “Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection”, Nature, Vol. 476, 189, 2011 (hereinafter referred to as Non-patent document 2). A magnetization switching method utilizing the spin-orbit coupling is to be described.
In FIG. 1, a magnetic body layer 120 is formed over an underlying layer 110, and a cap layer 130 is formed over the magnetic body layer 120. That is, the underlying layer 110, the magnetic body layer 120, and the cap layer 130 are stacked in this order. The stacking direction is a Z-direction and in-plane directions perpendicular to the Z-direction are an X-direction and a Y-direction. The X-direction and the Y-direction are perpendicular to each other.
The magnetic body layer 120 has perpendicular magnetic anisotropy. In FIG. 1, the direction of magnetization M in the magnetic body layer 120 is +Z-direction. Further, the magnetic body layer 120 is in contact at the lower surface with the underlying layer 110 and in contact at the upper surface with the cap layer 130. Materials for the underlying layer 110 and the cap layer 130 are different. In the example described in the Non-patent document 2, a stacked structure of the underlying layer 110/magnetic body layer 120/cap layer 130 is Pt/Co/AlO. Accordingly, characteristics of the interface between the magnetic body layer 120 and the underlying layer 110 are different from the characteristics of the interface between the magnetic body 120 and the cap layer 130. In other words, the magnetic body layer 120 has vertically “asymmetric” interfaces.
It is assumed that a current Iw in an in-plane direction (for example, in +X-direction) is supplied to the magnetic body layer 120. In this case, “Rashba effective magnetic field HR” is produced due to the spin-orbit coupling. The direction of the Rashba effective magnetic field HR is the direction of a cross product of the “asymmetric” direction (+Z-direction) and the direction of the in-plane current Iw (+X-direction), and this is +Y-direction in the example of FIG. 1.
Further, when an external magnetic field H is applied to the magnetic body layer 120 as illustrated in FIG. 2, the external magnetic field H and the Rashba effective magnetic field HR produce an effective magnetic field HE. The direction of the effective magnetic field HE is the direction of a cross product of the direction of the Rashba effective magnetic field HR and the direction of the external magnetic field H. As illustrated in FIG. 2, when the direction of the external magnetic field H is the +X-direction, an effective magnetic field HE in the −Z-direction is produced.
The magnetization M of the magnetic body layer 120 can be reversed to the −Z-direction by acting the thus produced effective magnetic field HE in the −Z-direction. Conversely, when the direction of the current Iw is set to the −X-direction, an effective magnetic field HE in the +Z-direction is produced. Magnetization M of the magnetic body layer 120 can be reversed to the +Z-direction by acting the effective magnetic field HE in the +Z-direction. That is, magnetization of the magnetic body layer 120 can be switched by switching the direction of the in-plane current Iw supplied to the magnetic body layer 120.
FIG. 3 is a schematic view illustrating a configuration of a device described in the Non-patent document 2. The stacked structure of the underlying layer 110/magnetic body layer 120/cap layer 130 is Pt/Co/AlO. The magnetic body layer 120 is formed over a portion of the underlying layer 110, and the current Iw is supplied to the magnetic body layer 120 by way of the underlying layer 110. Specifically, the current Iw is caused to flow between both ends of the underlying layer 110 and a portion of the current Iw is supplied to the magnetic body layer 120.